1. Field of the Invention
The present invention relates to a structure, manufacturing process and related circuit for a nano device transistor for a biosensor so as to achieve the object of detecting the specific species for bio measurement.
2. Description of the Prior Art
In the journal of “Science” published in 2001, Professor Charles M. Lieber, the professor of the chemical department of Harvard university, published a paper related to the manufacturing of the biological and chemical sensor by using nano wire. As shown in FIG. 1, the refurbished nano wire 10 is used for absorbing different anti-bodies 12. After the antigen 14 and the anti-body 12 are combined and absorbed on the surface of the nano wire, the relative polarization (dipole) effect of the electric charges in the molecule on the nano wire 10 is equivalent to the effect of forming a fixed bias on the surface of the nano wire. This bias will affect the energy band of the nano wire so that the status of the current conduction will be varied. By sensing the variation of the status of the current conduction, it can be detected whether the specific antigen exist. In addition, by changing the anti-body 12 initially absorbed by the nano wire 10, the different kind of the antigen 14 can be detected.
FIG. 2 is the perspective diagram of a prior art device structure for bio measurement. An oxidization layer 22 for insulation is positioned on a silicon substrate 21, and metal drain 23 and source 24 capable of electric conduction are deposited on the oxidization layer 22. A nano channel layer 25 is deposited between the drain 23 and the source 24 for conducting the drain 23 and the source 24. When performing the bio measurement, the object 26 to be detected is dripped to be positioned on the source and drain 23, 24 and the nano channel layer 25, and a fixed bias effect is formed on the surface of the nano channel layer 25 so that the status of current conduction between the source and the drain will be varied.
Generally, the prior art carbon nano tube and nano wire transistor have the characteristic of two-way conduction (ambipolar). Under the different absorbing concentration of the bio object on the surface of the carbon nano tube and the nano wire, the bias level of the threshold conduction voltage will be different because of the different polarization effects of the electric charges. Please refer to FIG. 3. FIG. 3 is the prior art voltage-current diagram. The horizontal axis represents the gate voltage (V), and the vertical axis represents the variation of the current (I) during the detection. When the gate voltage is controlled to be 0V during detection, compared with the original conduction characteristic (as shown by the original curve 31) when not detecting, the practical existence of the object to be detected will affect the conduction characteristic of the carbon nano tube and the nano wire transistor, but because of the characteristic of two-way conduction, the current maybe less than (as the first position 32), equal to (as the second position 33), or greater than the original current (as the third position 34). Therefore, when the number of the bio objects to be detected, which are absorbed on the surface, the misjudgment is easily happened.
In order to resolve the possibility of the misjudgment, it is necessary to use a nano device transistor having the characteristic of one-way conduction. This object can be achieved by rigidly controlling the impurity doping concentration of the carbon nano tube and the nano wire. However, the dependence on the stability of the manufacturing process is too great, and it is not easy to control the uniformity of the practical impurity doping concentration. Therefore, the conduction characteristic of the device will be affected. Thus, the present invention provides the structure and the manufacturing process of a nano device transistor for a biosensor so as to achieve the characteristic of one-way conduction. By applying this structure, the correct judgment for the signals can be achieved.
Furthermore, in order to conveniently detect the different polarized electric charges after the different objects to be detected are absorbed on the nano channel layer 25, the nano device transistor having the conduction characteristics of the p-type and n-type semiconductors provides the greater flexibility of the detection method. However, under the atmosphere, the carbon nano tube and the nano wire presents the characteristic of the p-type semiconductor. In order to manufacture the carbon nano tube and the nano wire having the characteristics of the n-type semiconductor, the inside oxygen has to be effectively excluded. For example, the annealing under the vacuum, or using the solution of alkali metal ions to dope the carbon nano tube, or using the in-situ doping method to dope the nano wire, and so on. However, the above methods are not effective, and the results are not good. The conductive currents for the manufactured n-type semiconductor carbon nano tube and the nano wire transistor are not large. Therefore, the present invention provides a structure and manufacturing process for a double-gate carbon nano tube and nano wire transistor having the tunable voltage-controlled p-type or n-type conduction characteristics. Therefore, the object of p-type or n-type conduction can be achieved without modulating and controlling the manufacturing process.
Since the professor Charles M. Lieber published the article related to manufacture the bio and chemical sensor by using the nano wires, many researches are devoted to apply the carbon nano tube and the nano wire transistor to detect the different bio and chemical objects. However, the structure and circuit for the nano device transistor is not mentioned. Therefore, the present invention provides a structure and manufacturing process of a nano transistor for a biosensor so as to improve the correctness and the judgment of the detection and achieve the design of the p-type and n-type tunable conduction. The present invention provides the effective solution to resolve the problems of the prior art, and apply the serial connection or parallel connection structure of the nano device transistor for the biosensor to promote the sensitivity of the detection.